1. Field of the Invention
The present invention relates to a video signal processing apparatus for quantizing video signals obtained from a plurality of solid-state image pickup devices for picking up an originating image substantially from image one direction and inputting them to a video RAM, and for performing a correlation computing operation on video signals between different video signal input systems by using quantized data in the video RAM. More particularly, the present invention relates to a video signal processing apparatus capable of absorbing and correcting variations of video signal levels caused by discrete factors of each input system.
2. Description of the Related Art
Generally, a video signal processing apparatus for picking up images originating substantially from one direction by using a solid-state image pickup device of a plurality of video signal input systems and for performing a correlation computing operation on video signals of each system has been applied to various fields. For example, when the video signal processing apparatus is applied to a running car, it is possible to perform automatic running control by detecting a motor vehicle running in front of one's car to measure the distance between one's car and the car in front so that the distance can be set to a target safe distance.
In this type of video signal processing apparatus, to enhance the reliability of the correlation computing operation, it is preferable that the density distributions of video signals obtained from a plurality of video signal input systems be matched with each other so as to make the characteristics between the video signal input systems uniform.
FIG. 4 is a block diagram illustrating a conventional video signal processing apparatus formed of two video signal input systems. In this figure, reference numerals 11a and 11b respectively denote first and second video signal input systems (hereinafter simply referred to as video signal input systems). As each of them has the same construction, only the block construction within one of the video signal input systems, 11a, is shown. Therefore, though not shown here, the other video signal input system 11b is assumed to be formed of elements designated by reference numerals 1b to 9b.
Reference numeral 1a denotes an optical system; reference numeral 2a denotes a solid-state image pickup element for photoelectrically converting an image picked up by the optical system 1a; reference numeral 3a denotes an amplifying circuit for amplifying charges discharged from the solid-state image pickup element 2a; reference numeral 4a denotes a solid-state image pickup device formed of the solid-state image pickup element 2a and the amplifying circuit 3a.
Reference numeral 5a denotes an amplifying circuit for amplifying a composite signal (a video signal including a synchronization signal), i.e., a video signal Va, output from the solid-state image pickup device 4a, to an AD conversion level; reference numeral 6a denotes a filter circuit for preventing folding strain at sampling time during AD conversion; reference numeral 7a denotes a clamping circuit for clamping the pedestal level of the video signal Va; reference numeral 8a denotes an AD conversion circuit for converting the video signal Va via the clamping circuit 7a into quantized data Da; and reference numeral 9a denotes a video RAM for inputting and storing the quantized data Da.
Reference numeral 10 denotes a video signal processing section for inputting quantized data Da and Db from the video RAM of the video signal input systems 11a and 11b, which section performs various computing operations such as a correlation computing operation between the quantized data Da and Db. A result C of the computing operation by the video signal processing section 10 is output to an external apparatus (not shown) as required.
As described above, to enhance the reliability of the result C of the computing operation of the video signal processing section 10, an automatic aperture control, for example, is applied to the optical system 1a, and characteristics output between the video signal processing apparatuses are made uniform by an AGC (Automatic Gain Control) circuit within the amplifying circuit 3a inside the solid-state image pickup device 4a of one of the video signal input system, 11a.
Further, the optical system 1a inside the video signal input system 11a is provided with an AGC function, or the level matching of each video signal Va is performed by manual gain control, so that characteristics variations between the video signal input systems 11a and 11b are reduced so as to suppress as much as possible an influence upon a correlation operation between the video signal input systems 11a and 11b caused by hardware.
Next, a description will be given of the operation of the conventional video signal processing apparatus shown in FIG. 4 by referring to one of the video signal input systems, 11a.
Initially, an image formed in the solid-state image pickup element 2a by an optical system 1 is amplified by the amplifying circuit 3a, and then output from the solid-state image pickup device 4a as the video signal Va. Further, the video signal Va is amplified by the amplifying circuit 5a, and then input through the filter circuit 6a and the clamping circuit 7a to the AD conversion circuit 8a.
The AD conversion circuit 8a converts the video signal Va into quantized data Da and stores it in the video RAM 9a. The quantized data Da in the video RAM 9a, together with the other quantized data Db, is input to the video signal processing section 10 were a correlation computing operation is performed, such as the computing operation result C indicating a distance up to an object is output to an external apparatus.
The conventional video signal processing apparatus, as described above, performs uniform adjustment control for each of the video signal input systems 11a and 11b in order to make the variations of the characteristics between the video signal input systems 11a and 11b uniform, and performs a correlation computing operation between the video signals Va and Vb of a plurality of video signal input systems. Therefore, problems arise, for example in that there is a need at a final stage to perform manual fine adjustments. Also deviations occur even after such fine adjustments are made, due to temperature and component aging, as a result of which a computing operation result C having high reliability cannot be obtained.